112 research outputs found
Bounds on Compactness for LMXB Neutron Stars from X-ray Burst Oscillations
We have modelled X-ray burst oscillations observed with the Rossi X-ray
Timing Explorer (RXTE) from two low mass X-ray binaries (LMXB): 4U 1636-53 with
a frequency of 580 Hz, and 4U 1728-34 at a frequency of 363 Hz. We have
computed least squares fits to the oscillations observed during the rising
phase of bursts using a model which includes emission from either a single
circular hot spot or a pair of circular antipodal hot spots on the surface of a
neutron star. We model the spreading of the thermonuclear hot spots by assuming
that the hot spot angular size grows linearly with time. We calculate the flux
as a function of rotational phase from the hot spots and take into account
photon deflection in the relativistic gravitational field of the neutron star
assuming the exterior spacetime is the Schwarzschild metric. We find acceptable
fits with our model and we use these to place constraints on the compactness of
the neutron stars in these sources. For 4U 1636-53, in which detection of a 290
Hz sub-harmonic supports the two spot model, we find that the compactness
(i.e., mass/radius ratio) is constrained to be M/R < 0.163 at 90% confidence (G
= c = 1). This requires a relatively stiff equation of state (EOS) for the
stellar interior. For example, if the neutron star has a mass of 1.4 Msun then
its radius must be > 12.8 km. Fits using a single hot spot model are not as
highly constraining. We discuss the implications of our findings for recent
efforts to calculate the EOS of dense nucleon matter and the structure of
neutron stars.Comment: 27 pages, 6 figures, AASTeX. Revised and expanded version.
Resubmitted to Astrophysical Journa
Using a Discrete Choice Experiment to Elicit the Demand for a Nutritious Food: Willingness-to-Pay for Orange Maize in Rural Zambia
Using a discrete choice experiment, this paper estimates the willingness to pay for biofortified orange maize in rural Zambia. The study design has five treatment arms, which enable an analysis of the impact of nutrition information, comparing the use of simulated radio versus community leaders in transmitting the nutrition message, on willingness to pay, and to account for possible novelty effects in the magnitude of premiums or discounts. The estimation strategy also takes into account lexicographic preferences of a subset of our respondents. The results suggest that (a) orange maize is well liked and can compete with white maize in the absence of a nutrition campaign, (b) there is a premium for orange maize with nutrition information, and (c) the mode of nutritional-message dissemination does not have a large impact on consumer acceptance, and (d) novelty effects do not translate into higher willingness to pay for orange maize.
Metal-insulator transitions in tetrahedral semiconductors under lattice change
Although most insulators are expected to undergo insulator to metal
transition on lattice compression, tetrahedral semiconductors Si, GaAs and InSb
can become metallic on compression as well as by expansion. We focus on the
transition by expansion which is rather peculiar; in all cases the direct gap
at point closes on expansion and thereafter a zero-gap state persists
over a wide range of lattice constant. The solids become metallic at an
expansion of 13 % to 15 % when an electron fermi surface around L-point and a
hole fermi surface at -point develop. We provide an understanding of
this behavior in terms of arguments based on symmetry and simple tight-binding
considerations. We also report results on the critical behavior of conductivity
in the metal phase and the static dielectric constant in the insulating phase
and find common behaviour. We consider the possibility of excitonic phases and
distortions which might intervene between insulating and metallic phases.Comment: 12 pages, 8 figure
A Structural and Algorithmic Study of Stable Matching Lattices of "Nearby" Instances, with Applications
A Structural and Algorithmic Study of Stable Matching Lattices of Multiple Instances
Recently MV18a identified and initiated work on the new problem of
understanding structural relationships between the lattices of solutions of two
``nearby'' instances of stable matching. They also gave an application of their
work to finding a robust stable matching. However, the types of changes they
allowed in going from instance to were very restricted, namely, any one
agent executes an upward shift.
In this paper, we allow any one agent to permute its preference list
arbitrarily. Let and be the sets of stable matchings of the
resulting pair of instances and , and let and
be the corresponding lattices of stable matchings. We prove
that the matchings in form a sublattice of both
and and those in form a join
semi-sublattice of . These properties enable us to obtain a
polynomial time algorithm for not only finding a stable matching in , but also for obtaining the partial order, as promised by Birkhoff's
Representation Theorem, thereby enabling us to generate all matchings in this
sublattice.
Our algorithm also helps solve a version of the robust stable matching
problem. We discuss another potential application, namely obtaining new
insights into the incentive compatibility properties of the Gale-Shapley
Deferred Acceptance Algorithm.Comment: arXiv admin note: substantial text overlap with arXiv:1804.0553
Bearing witness to the Covid-19 lockdown
During the lockdown, migrant workers have produced ‘proofs’ to lay claim to
promised aid, display grief and gratitude, and to archive violence they faced.
These fragments from the worker-as-witness throw up critical questions on
practices of welfare and aid
Caste, Kinship, and Life Course: Rethinking Women's Work and Agency in Rural South India
This paper reexamines the linkages between women's work, agency, and well-being based on a household survey and in-depth interviews conducted in rural Tamil Nadu in 2009 and questions the prioritization of workforce participation as a path to gender equality. It emphasizes the need to unpack the nature of work performed by and available to women and its social valuation, as well as women's agency, particularly its implications for decision making around financial and nonfinancial household resources in contexts of socioeconomic change. The effects of work participation on agency are mediated by factors like age and stage in the life cycle, reproductive success, and social location – especially of caste – from which women enter the workforce
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